1. Technical Field
The invention relates to a process for drilling into a subterranean hydrocarbon-bearing formation and more particularly to a process for minimizing lost circulation of a drilling fluid when drilling into a subterranean hydrocarbon-bearing formation.
2. Background Information
A drilling fluid is a fluid which is circulated from an earthen surface down through a drilled out wellbore to a drilling face and back to the surface when drilling into a subterranean formation which contains hydrocarbons. Drilling fluids are specifically designed to perform a number of functions, including cooling and lubricating the drill bit, removing drill cuttings from the wellbore, supporting the weight of the drill pipe and drill bit, providing a hydrostatic head to maintain the integrity of the wellbore walls, preventing significant flow of fluids across the wellbore face into the wellbore and vice versa.
The most common conventional drilling fluids known in the art are termed "drilling muds", which are dispersions of solid particles in a liquid. Examples of drilling muds are aqueous dispersions of clays (e.g. bentonite) and/or gypsum. Drilling muds also commonly contain one or more polymeric additives in an effort to control "lost circulation", which is the excessive flow of drilling fluids across the wellbore face out of the wellbore and into the formation. See, for example, U.S. Pat. Nos. 4,740,319 to Patel et al, 4,726,906 to Chen et al, 4,675,119 to Farrar et al and 4,282,928 to McDonald et al. Solutions containing materials, such as polymeric additives, which inhibit the flow of drilling fluids from the wellbore into the formation, are termed "lost circulation fluids".
The drilling art reflects an on-going evolution to develop lost circulation fluids which effectively control lost circulation under a broad range of operating conditions. Many lost circulation fluids known in the art are unsatisfactory because of operational limitations restricting their utility. For example, some lost circulation fluids are ineffective in the presence of high salt concentration brines. Others undergo thermal degradation when subjected to high operational temperatures. The most significant shortcoming is the lack of lost circulation fluids in the art, which effectively control lost circulation encountered when drilling through voids occurring in the formation.
Thus, a need exists for a lost circulation fluid which effectively prevents or reduces lost circulation of drilling fluid under the broadest range of operating conditions encountered. Specifically, a need exists for a lost circulation fluid which not only minimizes lost circulation into competent formation rock, but which has sufficient strength and integrity to minimize lost circulation into voids in direct communication with the wellbore, such as fractures and fracture networks.